Combined thermal reforming, catalytic cracking and hydrofining process to improve engine cleanliness



March 10, '1959 R. c. MORBECK ETAL 2,877,172 7 COMBINED THERMAL REFORMING. CATALYTIC CRACKING AND HYDROFINING PROCESS TO IMPROVE ENGINE CLEANLINESS Filed July 14,

Robert C. Morbeck Stanley OBronson Znventors j SumnenBSweetser 13 m), 07%,; Qttorney United States Patent 0.

COMBINED THERMAL REFORMING, CATALYTIC CRACKING AND HYDROFINING PROCESS TO IMPROVE ENGINE CLEANLINESS Robert C. Morbeck, Fanwood, Stanley 0. Bronson II, Mountainside, and Sumner B. Sweetser, Cranford, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application July 14, 1952, Serial No. 298,656

7 Claims. (Cl. 208-79) The present invention is concerned with the production of high quality petroleum oil products. The invention is more particularly concerned with the treatment of cracked petroleum oil fractions boiling below about 700 F. by a controlled, mild hydrofining operation. In accordance with the present invention thermally or catalytically cracked petroleum hydrocarbons, especially those boiling below about 430 F. are hydrofined whereby the resulting product comprises a fuel having improved engine, cleanliness. The hydrofining operation is conducted so as to give a reduction in bromine number not greater than about 20%.

It is well known in the art to refine petroleum fractions for the production of high quality gasolines, kerosenes, and diesel fuels by various procedures. For example, it is known to treat petroleum fractions boiling in the motor fuel boiling range with sulfuric acid and with various other reagents. While the use of sulfuric acid produces a satisfactory product, in many operations, particularly when the feed oil comprises a cracked stock, a relatively high polymerization loss results. Furthermore, when the concentration of undesirable constituents is relatively high, it is necessary to use rather large quantities of acid which necessitates further refining of the acid treated oil after removal of the treating acid. In addition, the acid must be recovered and reconcentrated or otherwise restored. It has now been discovered that providing the cracked constituents of a motor fuel blend are hydrofined in a controlled manner, the quality of the fuel particularly with respect to engine cleanliness characteristics is materially improved. By the present process wherein cracked petroleum hydrocarbons boiling in the motor fuel boiling range are hydrofined, the same are substantially completely freed of undesirable constituents which cause corrosion, varnish andvalve deposits in an internal combustion engine. Sludge deposits in the lubricating oil are also avoided.

The process of the present invention may be more fully understood by reference to the drawing illustrating an embodiment of the same.

Referring specifically to the drawing, a crude oil feed stock is introduced into distillation zone 1 by means of feed line 2. Temperature and pressure conditions in zone 1 are adapted to remove overhead by means of line 3 normally gaseous hydrocarbons. Constituents boiling in the light naphtha boiling range are removed by means of line 4, while hydrocarbons boiling in the heavy naphtha boiling range are removed by means of line 5. A heating oil fraction is removed by means of line 6, while a gas oil fraction is removed by means of line 7. A residuum fraction is removed by means of line 8.

In accordance with the present invention the heavy naphtha fraction removed by means of line 5 is passed to a thermal cracking or reforming zone 9. In this zone the oil is raised to a temperature in the range from about 850 to 1050 F. and held at a pressure in the range from about 250 to 1000 lbs. p. s. i. g. The operating conditions are adapted, that is, time, temperatureand 2,877,172 Patented Mar. 10, 1959 pressure, to crack the feed and to produce a higher octane number product. The cracked or reformed product is removed from thermal cracking zone 9 by means of line 10 and passed into a distillation zone 11. Temperature and pressure conditions in zone 11 are adapted to segregate a gas by means of line 12, a light thermal naphtha by means of line 13, a heavy thermal naphtha by means of line 14 and a higher boiling fraction which is removed from zone 11 by means of line 15.

In accordance with the present invention the gas oil fraction removed by means of line 7 is passed into a catalytic cracking zone 16, wherein the same is subjected to a catalytic cracking conditions, in the presence of a suitable catalyst, as, for example, alumina or magnesia. Temperatures in the catalytic cracking zone are in the range of about 800 F. to 1100 F., while pressures are in the range from about 5 to lbs. p. s. i. g. The catalytically cracked product is removed from zone 16 by means of line 17 and passed into a fractionating zone 18. Temperature and pressure conditions in zone 18 are adapted to segregate a gas which is removed by means of line 19, a catalytically cracked light naphtha which is removed by means of line 20, a catalytic heavy naphtha which is removed by means of line 21, and a heating oil fraction segregated by means of line 22. A higher.

boiling fraction is removed by means of line 23.

In accordance with the present invention the heavy thermal naphtha segregated by means of line 14 and the catalytically cracked heavy naphtha segregated by means of line 21 are passed to hydrofining zone 24, wherein the same is mildly hydrofined. The hydrofined product is removed from zone 24 by means of line 25' and passed into a caustic washing or steam stripping zone 26.

The hydrofined product is removed from zone 26 by means of line 27, and preferably combined with the other segregated naphtha fractions.

It is also within the concept of the present invention to hydrofine under certain conditions the light catalytic naphtha segregated by means of line 20. If this mode of operation be utilized, the light catalytic naphtha is passed into hydrofining zone 28 by means of line 29. The hydrofined product is removed from zone 28 by means of line 30 and passed into a caustic washing or steam stripping zone 31. The finished product is withdrawn from zone 31 by means of line 32 and preferably blended with other naphtha streams.

It is essential, in practicing the present invention that the hydrofining operation conducted on the cracked oil be a mild hydrofining operation. This is to be distinguished from conventional hydrofining operations heret-ofore practiced in the art. Such hydrofining operations have been employed at pressures from 200 to 500 lbs. p. s. i. g., at feed rates of .5 to 2.0 volumes of feed per volume of catalyst per hour. Relatively high rates of hydrogen recycle have been employed as for example, 2,000 to 4,000 standard cu. ft. per barrel in order to prevent carbonization of the catalyst. Likewise, very active catalysts have been used which are effective for desulfurization. Under these conditions hydrogen consumption has generally been in the range of 150 to 600 standard cu. ft. per barrel of feed. This relatively high consumption of hydrogen in the past has made the process expensive to operate, so that its application in the past has been limited to the treatment of relatively high sulfur stocks which could not be desulfurized by any other available treating operation. The catalyst heretodesulfurizes to a great extent, conventional hydrofining operations have not generally been necessary in the processing of cracked oils.

The mild hydrofining conditions of the present invention may be secured by lowering the temperature, increasing the feed rate per volume of catalyst or by using a less active catalyst. In accordance with the present invention the temperatures used are in the range from about 400 to 700 F, preferably in the range from about 500 to 650 F. Pressures employed are in the range from 50 to 250 lbs. p. s. i., preferably in the range from about 100 to 200 lbs. p. s. i. The feed rates, in accordance with the present process, are in the range from about 120 volumes of liquid per volume of catalyst per hour. Preferred feed rates are in the range from 6-16 v./v./hr. The hydrogen in the gas to the hydrofining unit may vary from 50 to 100%. This means that, for example, dilute hydrogen from a hydroformer can be used in the hydrofining process. A particularly desirable method of hydrofining in accordance with the present process is to recycle appreciable quantities of hydrogen to the hydrofining unit in order to completely prevent carbonization of the catalyst.

The catalyst utilized in the present operation may comprise known hydrofining catalyst, as for example, cobalt molybdate on a carrier as for example, alumina, providing other operating conditions are adjusted to secure a mild hydrofining process. The amount of cobalt molybdate employed is about to 13% by weight based upon the weight of the alumina.

The catalyst is prepared by known methods, such as by impregnation of the alumina with an ammoniacal solution of cobalt and molybdenum salts. The catalyst is dried and decomposed to convert the cobalt and molybdenum salts to the oxides. I

Other catalysts may be employed, as for example, a mixture of tungsten sulfide and nickel sulfide.

it is to be understood that the mild hydrofining conditions of the present invention are secured by the adjustment of the above named operating conditions. For instance, it a relatively high liquid feed rate'is used as compared to the amount of catalyst present, the higher temperature range may be employed. On the other hand, if a very active catalyst is used, it is desirable to use a relatively high feed rate or to use a relatively low temperature. The mild hydrofining conditions of the present invention are measured by the amount of hydrogen consumption per barrel of oil feed. As pointed out heretofore in the art, conventional hydrofining operations utilized for the desulfurization of certain stocks are conducted under conditions whereby the hydrogen consumption ranges from 150 to 600 standard cu. ft. of hydrogen per barrel of oil. These operations used heretofore in the art secured a substantial sulfur reduction (50 to 90%). In accordance with the present process, operating conditions are adjusted so that the hydrogen consumption in standard cu. ft. per barrel does not exceed 60 and is preferably less than 40.

A very desirable method of measuring the hydrofining conditions is to so control the variable factors so that the reduction in bromine number is not greater than about 20%. As pointed out above in the operation of gasoline engines on fuels containing cracked components, there is a decided tendency for varnish'to deposit on the'piston and for sludge to be deposited in the lubricating oil. This tendency for sludge to deposit is particularly pronounced in stop and go driving such as is encountered in the operation of delivery trucks and local busses. This deposition of sludge in the oil tends to clog oil lines and streams and thus impair the operation of the lubricating system in the engine.

The sludge-forming tendency of' the cracked naphthas is dependent to a considerable extent on the'boiling range; the heavy cracked naphthas being much worse offenders than'the light naphthas, that is, cracked naphthasboilingthe range from about 250 F. to 430 F. Also, as

pointed out heretofore, acid treating is one method which has been found 'to be eifective'in reducin'g'the"s1ud'ge= forming tendency of cracked naphthas used in gasolines.

For example, treats of two to twelve pounds of 75-80% 5 acid per barrel of naphtha, have proved effective in reducing sludge forming tendencies. However, acid treating is an expensive operation involving batch treats with treating losses of about '2 to Furthermore, recovery and regeneration of the acid is an expensive operation and frequently contributes to atmospheric pollution.

The present invention is concerned with the use of mild hydrofining as a new means of improving the engine cleanliness characteristics of cracked naphthas. The effectiveness of mild hydrofining for this purpose has been demonstrated by engine tests.

The process of the present invention will be more fully understood by the following example illustrating the same:

EXAMPLE 1 A naphtha obtained by thermal reforming a virgin naphth and having a boiling range of 27542 8"F.' was hydrofined over cobalt molybdate catalyst supported on alumina. The temperature was 565 F., the feed rate 8.5 v./v./hr., and the pressure 200 p. s. i. g. The hydrogen rate including recycle was 1000 cu. ft. per barrel of feed. Inspections on the feed and on the product after caustic washing for hydrogen sulfide removal are shown in the following tabulation:

1 Centigrams oi bromine per gram.

2 Equivalent milligrams paratertiary amyl phenol per 100 cc.

3 Milligrams bromine per gram.

4 The riiazonium fiuoboratc deposit factor is an index of the engine cleanliness characteristics of a motor fuel. This test utilizes the coupling reaction which takes place between diazotiscd p-nitranilme fiuoboratc and certain unsaturated compounds (which cause engine fouling) to form acoiored compound. Intensity of color formed after a given time interval is taken as an index of the deposit forming compounds present. In running the test the fraction of the sample boiling over 275 F. and purified by treatment with dilute acid and alkali and steam distillation to 3% bottoms is used. A known quantity of this fraction is added to a solution of p-nitrauilino diazonium fiuoborate (N O2GaHiN=NB F4) in acetone and the optical density measured at intervals in a Hellige-Diller photometer. The optical density is plotted against time and the value after 20 minutes read from the curve. The optical density multiplied by the ratio of the fractionboiling over 275 F. to the whole sample gives the diazouium fluoborate deposit factor.

- Differential octane ratings.

The mildness of the hydrofining conditions used is evident from the fact that the bromine number was re duced only from 18 to 15 and there was no loss in the leaded octane number of the treated product. The phenol number, the diene number, the ultraviolet absorptivity and the diazonium fluoborate deposit factor indicated that the fuel had substantially improved engine cleanliness characteristics. The above example illustrates that mild hydrofining is effective in improving engine cleanliness'characteristics. it is very important that the hydrofining conditions be maintained mild in order to prevent loss in octane number on the product.

The only positive test available to demonstrate engine cleanliness is an engine test itself. The preferred test for determining sludge forming tendency is designed to simulate stop-and-go driving. in this test, the engine is oper ated' intermittently at high and low speeds. It is impracticable to run the test on heavy naphthas alone. Such naphthas aregenerally blended with virgin naphthas and butane, which have excellent'engine' cleanliness characteristics, in order to obtain a blend of suitable volatility for testing."Both the raw and the hydrofined thermal reformates were tested in blends containing 46% reformate, 4% butane and 50% of light virgin naphtha.

The results of the engine test are expressed on the basis of demerit rating, the higher the demerit rating, the dirtier the gasoline. The rating is based on visual appearance of various parts of the engine. The demerit rating on the blend containing the raw thermal reformate was 1.6, compared to 0.6 on the blend containing the hydrofined reformate. These values are representative of very dirty and very clean gasolines, indicating that mild hydrofining of the thermal reformate had produced a marked effect on engine cleanliness characteristics.

Other'operations were conducted wherein hydrofining tests of different severity were conducted. The results of these operations are as follows:

Table II that temperature can be used to increase the severity of the hydrofining.

For the operations described in columns H, I, and I, a new sample of catalyst was used which had the same composition as the catalyst used in columns B through G, but had a slightly higher activity. When the thermal reformate feed stock was treated with this catalyst at 595 and 5.9 v./v./hr., the bromine number of the product was 8, indicating that excessive saturation of olefins had taken place. In an attempt to alleviate this situation, the feed rate was increased to 7.8 v./v./hr., but this raised the bromine number to a value of 10 which was still lower than desirable. A further change in operating conditions was made to reduce the temperature from 595 to 565 F., and to increase the feed rate to 8.5

HYDROFINING THERMAL REFORMATE (250 F. TO 430 F.) [Cobalt molybdate catalyst, 200 p. s. i. g.]

Column A B G D E F G H I I Feed Catalyst Sample A. B

Operating Conditions:

Temperature, F.-- 600 600 600 600 Feed Rate, v./v./hr 1 4 8 16 Fresh H1, s. 0. F. B 200 200 200 200 Hi Purity, Percent 70 70 70 70 Total 11,, s. C F. B 1, 000 1, 000 1,000 1, 000 Product Inspections:

Bromine N o. cgs./g 18 4 12 16 16 Diene No 1. 32 0 0.10 0.13 0. 50 'Dlszoulum Fluoborate-- Optical Density 0.33 0 0 0.0 0.07 Deposit Fact0r 0 0 2. 6. 9 Phenol No 390 3 15 98 Sulfur, Wt. Percent 0. 050 0. 010 0.019 0. 030 0.033 0. 04 OFRR Octane No;

Clear 75.6 69.4 73.9 75.0 75.3 72.4 73.7 71.9 73.1 75.0 200. TEL 84.5 81.7 84.3 84.4 84.5 82.7 34,5 83.2 83.9 84.1

In practicing the present invention it is desirable that v./v./hr. At these operating conditions the bromine the hydrofining conditions are such that little or no loss number was brought to 15 which is considered a satisof octane number results. In the hydrofining operation factory level for this operation. These changes illusolefins are converted to paraflins and this tends to reduce trate the variables which can be changed to achieve the octane number. On the other hand, sulfur is removed desired mild hydrofining conditions. 7 In general, it is from the product so that the lead susceptibility is indesirable to adjust the hydrofining conditions so that the creased, and this tends to raise the leaded octane number bromine number reduction is limited to about 33%, and of the product. It is important to so adjust the condipreferably to about 20% to assure minimum loss in tions that the loss of octane number by conversion of leaded octane number. In Table II the feed stock used olefins to paraifins is substantially balanced by the imwas a heavy thermal reformate obtained by thermal reproved lead susceptibility of the hydrofined product. Reforming of a heavy virgin naphtha. The invention may ferfing column B of Table II, it is pp that When also be practiced using a heavy catalytic naphtha, for thermal reformate was hydrofined at 600 F., a feed rate example, one produced by. fluid catalytic cracking of a of 1 v./v./hr. bromine number was reduced from 18 to 4, heavy gas oil. Hydrofining results obtained with a feed and sulfur from .05 to .016 weight percent. The overall f this type ar h w i T ble III, result of this change was that the leaded octane number was reduced from 84.5 to 81.7. In columns D and B Table [I] it is apparent that when the feed rate was increased to I v 8 or 16 v.-/v./hr., the bromine number was reduced only HYDROFINING HEAVY CATALYHG NAPHTHA to 1 5 to l6 and the sulfur to .030 to .038. The leaded [194 F. to 437 F.] octane number of the products from these operations was identical of that of the feed showing that the loss in Feed Rate, v.lv./hr Feed 1 4 a octane number from conversion of olefins to paraflins had been substantially counterbalanced by the increased lead Br i mine :Iumber 0 32 3 1 2 1 susceptibility resulting from sulfur reduction. It is this gi ggfg ggf gg 3 1 1 1 balance of conditions with which the invention is pri- 18 g 16 0 0 3 'marily concerned. The operating conditions illustrated fff ff f' 925 8m 8M M4 in column C are intermediate between those shown in 96.1 93.6 95.0 05.1 columns B and D and the results as illustrated by bromine number, sulfur removal and leaded octane number 211). UOP $5 inh b are likewise intermediate. Comparison of columns B and F shows that by operating at 500 F. in place of 600 F., As the feed rate was increased from 1 to 8 v./v./hr., a substantially higher bromine number is obtained. Comromin n m r a m r f m 6 w 17, nd lf r parison of columns G and D shows that by increasing the from t0 Welght Percent the Operatlon of 8 temperature to 700 F. by maintaining feed rate constant, 7 v./v./hr., the leaded octane number of the product was the bromine number of-the product is reduced illustrating 95.4 compared to 96.1 for the feed, showing that the '7 mildest type of hydrofining showed the smallest loss in octane rating.

' While the operation has been described with respect toheavy cracked naphthas, it is also very desirable for the treatment of light naphthas secured from a catalytic cracking operation boiling in the range from about 130 F. to 330 F. It has been discovered that if this particular naphtha is hydrofined as described, the combustion chamber deposits are materially reduced.

EXAMPLE II A number of operations were carried out wherein a catalytically cracked light naphtha was hydrofined as described. The results of these operations are as follows:

Table IV HYDROFINING CATALYTIC LIGHT NAPHTHA (130 F.- 330 F.) OVER COMBO; CATALYST- Operation 1 2 i 3 Catalyst Age, Hours 128 134 Operating Conditions:

Temperature, F 000 60 Feed Rate, v.[Hr./v 1 Feed 4.0 15. 7

Hz Rate, 8. C. F./B 1, 000 1,000 1,000

(Nominal) (Nominal) (Nominal) Pressure, p. s. i. g I 200 200 Product Inspections:

Bromine Number, cgs/gm- 91 55 80 Sulfur, wt. percent- 0. 14 0. 049 0.110 CFRR OctaneNumber Clear 93. 5 s8. 6 92. 1

+2 cc. TEL 97. 7 95.3 97.0

The results shown in column 2 of Table IV show that when hydrofining at a feed rate of 4 v./v./hr., bromine number was reduced from 91 to 55 and sulfur from .14 to 0.49. Under these conditions the leaded octane number of the product was 2.4 units lower than that of the feed. As shown in column 3 when the feed rate was in-.

creased to 15.7 v./v./hr., the bromine number was reduced only to 80 and sulfur to .110 weight percent. The product obtained under these conditions had a leaded octane number only 07 unit less than that of the feed. These data illustrate that mild hydrofining can be applied to light cracked naphthas as well as to heavy cracked naphthas with substantially no loss in octane number provided conditions are carefully regulated to minimize conversion of olefins to paraffins as measured by loss in bromine number.

What is claimed is:

1. Process for the production of a high quality motor fuel which comprises distilling a crude oil to segregate a hydrocarbon fraction boiling in the range from about 100 F. to 330 F., a hydrocarbon fraction boiling in the range of about 250 F. to 430 F., and a hydrocarbon fraction boiling in the gas oil boiling range, thermally reforming said hydrocarbon fraction boiling in the range from about 250 F. to 430 F., distilling the product from said thermal reforming operation to segregate a light thermal naphtha fraction and a heavy thermal naphtha fraction, hydrofining said heavy thermal naphtha fraction under conditions to secure a bromine number reduction of less than 20%, catalytically cracking said gas oil fraction to produce a catalytically cracked naphtha, thereafter blending said naphtha fraction boiling in the range from 100 F. to 330 F., said light thermal naphtha, said hydrofined heavy thermal naphtha, and said catalytic naphtha, whereby a high quality gasoline blend having improved engine cleanliness characteristics is secured.

2. Process for the production of hydrocarbon constituents boiling in the motor fuel boiling range having improved engine cleanliness which comprises distilling a crude oil to segregate a hydrocarbon fraction boiling in the heavy'naphthaboiling range, reforming said fraction under conditions to raise the octane number thereof, thermally distilling said fraction to secure a light" thermal naphtha anda heavy thermal naphtha, thereafter hydrofining said heavy thermal naphtha in the presence of extraneously generated hydrogen, at a temperature in the range of 400 to 700 F., at a pressure in the'range of 50 to 250 pounds per square inch, at a throughput of about 1 to 20 v./v.hr., employing a catalyst selected'from the group consisting of cobalt molybdate on acarrier, cobalt oxide, molybdenum oxide, tungsten sulfide and nickel sulfide, under conditions to secure a positive consumption of hydrogen not in excess of 60 standard cubic feet per barrel securing a bromine number reduction of less than 20%.

3. Process as defined by claim 2 wherein said heavy thermal naphtha boils in the range fromgabout 250 F. to 430 F.

4. Process for the production of hydrocarbon constituents boiling in the motor fuel boiling range having improved engine cleanliness which comprises distilling a crude oil to segregate a hydrocarbon fraction boiling in the gas oil boiling range, catalytically cracking saidf'raction under conditions to secure hydrocarbon constituents boiling in the motor fuel boiling range, distilling said latter fraction to secure a light catalytic naphtha and a heavy catalytic naphtha, thereafter hydrofining said heavy catalytic naphtha in the presence of extraneou'sly generated hydrogen, at a temperature in the range of 400 to 700 F, at a pressure in the range of 50 to 250 pounds per square inch, at a throughput of aboutl to 20 v./v./hr'., employing a catalyst selected from the group consisting of cobalt molybdate on a carrier, cobalt oxide, molybdenum oxide, tungsten sulfide and nickel sulfide," under such conditions to secure a positive consumption of hydrogen not in excess of 60 standard cubic feet per barrel securing a bromine number reduction of less than 20%.

5. Process as defined by claim 4 wherein said heavy catalytic naphtha boils in the range from about 250 to 430 F.

6. Process for the production of hydrocarbon constituents boiling in the motor fuel boiling range having improved combustion chamber characteristics which comprises distilling a crude oil to segregate a hydrocarbon fraction boiling in the gas oil boiling range, thereafter catalytically cracking said gas oil to produce hydrocarbon constituents boiling in the motor' fuel boiling range, segregating a light hydrocarbon fraction from said constituents, thereafter hydrofining said light fraction in the presence of extraneously generated hydrogen, at a temperature in the range of 400 to 700 F., at a pressure in the range of 50 to 250 pounds per square inch, at a throughput of about 1 to 20 v./v.hr., employing a. catalyst selected from the group consisting of cobalt molybdate on a carrier, cobalt oxide, molybdenum oxide, tungsten sulfide and nickel sulfide, under conditions to secure a positive consumption of hydrogen not in excess of 60 standard cubic feet perbarrel securing a bromine number reduction of less than 20%.

7. Process as defined by claim 6 wherein said light fraction boils in the range from about to 330 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,579 Cole Jan. 8, 1946 2,4133 12 Cole Dec. 31,1946 2,417,308 Lee Mar. 11, 1947 2,440,673 Jones May 4, 1948 2,516,876 Horne et a1. Aug. .1, 1950 2,542,970 Jones Feb. 27, 1951 2,574,451 Porter et al Nov. 6, 1951 2,620,362 Stiles Dec. 2, 1952 2,694,671 Baumgarten et al Nov. 16, 1954 2,717,860 Rex Sept. 13, 1955 2,717,861 Baurngarten et al Sept. 13, 1955 

1. PROCESS FOR THE PRODUCTION OF A HIGH QUALITY MOTOR FUEL WHICH COMPRISES DISTILLING A CRUDE OIL TO SEGREGATE A HYDROCARBON FRACTION BOILING IN THE RANGE FROM ABOUT 100*F. TO 330*F., A HYDROCARBON FARACTION BOILING IN THE RANGE OF ABOUT 250*F. TO 430*F., AND A HYDROCARBON FRACTION BOILING IN THE GAS OIL BOILING RANGE, THERMALLY REFORMING SAID HYDROCARBON FRACTION BOILING IN THE RANGE FROM ABOUT 250*F. TO 430*F., DISTILLING THE PRODUCT FROM SAID THERMAL REFORMING OPERATION TO SEGREGATE A LIGHT THERMAL NAPHTA FRACTION AND A HEAVY THERMAL NAPHTHA FRACTION, HYDROFINING SAID HEAVY THERMAL NAPHTHA FRACTION UNDER CONDITIONS TO SECURE A BROMINE NUMBER REDUCTION OF LESS THAN 20%, CATALYTICALLY CRACKING SAID GAS OIL FRACTION TO PRODUCE A CATALYTICALLY CRACKED NAPHTHA, THEREAFTER BLENDING SAID NAPHTHA FRACTION BOILING IN THE RANGE FROM 100*F. TO 330*F., SAID LIGHT THERMAL NAPHTHA, SAID HYDROFINED HEAVY THERMAL NAPHTHA, AND SAID CATALYTIC NAPHTHA, WHEREBY A HIGH QUALITY GASOLINE BLEND HAVING IMPROVED ENGINE CLEANLINESS CHARACTERISTICS IS SECURED. 